What do we know about vocal communication of emotion between different species of terrestrial tetrapods?

Investigating how animals perceive and interpret emotional signals across a variety of species is essential for deepening our understanding of the complexities underlying animal communication and social behaviour. Empirical evidence suggests that many animal species can extract valuable, contextually relevant information from their acoustic environments, including vocalisations produced by heterospecific organisms in their vicinity. This review examines the cross-species perception of vocal emotional expressions among terrestrial tetrapods, demonstrating that many of these animals recognise a range of emotions in the vocalisations of other species in a manner qualitatively similar to their perception of conspecific emotions. First, we outline the diverse methodologies employed to assess emotion perception, including behavioural and vocal responses, psychoacoustic playback experiments, physiological analyses linked to the autonomic nervous system, and neural imaging techniques. Then, we explore the relationships between emotional valence and arousal with various acoustic features of animal vocalisations such as fundamental frequency (perceived as pitch), harshness resulting from non-linear acoustic phenomena, call duration, and inter-call intervals. Lastly, we evaluate potential factors influencing the accuracy of cross-species emotion perception. Notably, familiarity with the vocalising species and domestication are identified as potential enhancers of cross-species emotion recognition. This review highlights significant research gaps, particularly in understanding how specific acoustic parameters shape emotion perception in interspecies vocal communication, and a heavy bias toward human subjects. Advancing knowledge in this domain is crucial, as it will not only deepen our understanding of emotional expression and perception across species but also provide broader insights into the evolution of animal communication.